A kite the size of a football field will provide most of the power for a German heavy freight ship set to launch in December.

The Beluga shipping company that owns the 140-metre 'Beluga' said it expects the kites to decrease fuel consumption by up to 50 percent in optimal cases as well as a cutback of the emission of greenhouse gases on sea by 10 to 20 percent. Interestingly, the ship will be hauling windmills from Esbjerg, Denmark to Houston, Texas.

The company that makes the kite for the German transport, SkySails, has made kites for large yachts but is targeting commercial ships with new, larger kites. And it has the ambitious goal of equipping 1,500 ships with kites by 2015.

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The SkySails system consists of a towing kite with rope, a launch and recovery system and a control system for the whole operation. The control system acts like the autopitot systems on an aircraft, the company says. Autopilot software sends and receives data about the sail etc to make sure the sail is set at its optimal position.

The company also says it provides an optional weather routing system so that ships can sail into optimal wind conditions.The kites typically fly at about 1,000 feet above sea level, thereby tapping winds that can be almost 50 percent stronger than at the surface.

Skysail isn't the only company pioneering kite technology. A US company, KiteShip, in Martinez, Calif., has been building ultra-large kites mostly for the private yachting sector, with plans to expand into cargo and cruise vessels.

Not everyone is sold on the kites however. In an article in the Atlanta Journal Constitution today, John Barnes, editor of Marine Engineers Review, a marine engineering magazine in London, said the jury's still out on kite propulsion systems. 'This could work, but there is an extra cost entailed, and it won't make much sense if the price of fuel falls back,' he said. 'It seems to be a practical approach, but we still need to see what the benefits and penalties will be.' One hurdle is the costs associated with the hiring of crews to actually tend the kites. Another: drawback: The system obviously won't work in a head wind, the article stated.